Lauer also asked Costolo how to tweet well and what he saw as the cardinal sin of tweeting.

While Costolo didn't give any concrete advice on how to become a Twitter superstar ("Everybody has their own language!"), he warned about not being genuine.

"In this day and age, with the ubiquity of communication we now have, people can sense inauthenticity very, very quickly," he said. "Authenticity is absolutely the key to a great tweet."

Costolo also said that to grow its user base, Twitter needs to bring media like photos and videos forward, while pushing back the "opaque language" that can be confusing for newbies. (Think of all the Twitter jargon like "RT" and "MT" that early adopters use.)

His idyllic goal for the service: That "everyone can come to Twitter and feel like it's a clean, well-lit place, and a global town-square."